Paving



Patented Jan. 2, 1940 UNITED sTATEs PATENT OFFICE PAvnvG ApplicationDecember as, 1936, serialv N.117Jzs5 1 claim. (ci. iiizar This inventionrelates to paving.

'I'he general object of the invention is to provide a paving whichincludes roadbed material united with a bituminous binder in a novelmanner. l

Another object of the invention is to provide a pavementincluding'roadbed material treated with successive applications ofbituminous material to produce a structure wherein the rela- 0 tiveamount of the binder decreases as the distance from the wearing surfaceincreases.

A specic object of my invention is to provide a roadbed material whichis treated with a plurality of applications of asphalt, oil, tar, etc.,

which penetrates, during the different applications, to diierent depthsinto the roadbed material.

Another object of the invention is to provide a road built up of aplurality of homogeneous zones with the densest zone nearest the surfaceand with a gradually diminishing density below the surface.

Another object of the invention is to provide a novel method of making aroad.

Other objects andthe advantages of my invention will be apparent fromthe following description taken in connection with the accompanyingdrawing, wherein:

Fig. 1 is a perspective View `with parts broken away showing a roadembodying the features oi my invention;

Fig. 2 is a diagrammatic section showing my invention;

Fig. 3 is an enlarged sectional detail showing the various zones;

Figs. .4, 5, 6 and 'I are diagrammatic sections taken on lines -I, 55,6--6 and' 'l-'l respectively Fig. 3;

Fig. 8' is a diagram showing the manner in which successive coatings areapplied; and

Fig. 9 is an enlarged section through a piece of road making materialshowing successive coatings thereon.

Referring to the drawing by reference characters I have shown myinvention as embodied in a road which is indicated generally at I0.

In the following specication I will refer to my invention as used inconnection with roads or pavements but it will be understood that myinvention may be used in general roadway, railway, dam, ditch or otherconstructions and may be used on horizontal surface, slopes, burms,etc., without departing from the spirit of my inven- 1 tion.

In the .prctice of my invention I may employ natural gravel or otheraggregate which is already in the .roadway and this material may be leftundisturbed or may be loosened before being treated according Ato myinvention. If desired, the aggregate may be transported tothe roadway.

The binder preferably consists of hard asphaltum, liquid asphaltic roadoils,.`or tar in various forms which is cut back with a light volatilesolvent in suicient amount t'o produce a mixture `.having a desiredpredetermined viscosity.

The solvents 'employed are preferably those which readily dissolveasphalts and tars and which have low viscosity at temperatures rangingfrom to 120 Fahrenheit. Such vsolventsmay be kerosene, cleaning solvent,gasoline, etc. These solvents have varying distillation ranges most ofwhich have an initial and end point between 175 `and 550 Fahrenheit.

If according to my invention a slow curing cut back is desired, I mayvemploy a straight residuum road oil having an asphalt content ofapproximately mixed with kerosene in the proportions of 25% to 35%kerosene to 75%.

to 65% road oil. For medium curing cut back a liquid asphalt having anormal penetration of to 400 is mixed with kerosene in the proportionsof 40 to 60 kerosene to 60 to 40 asphalt. For rapid curing cut back Imay employ a steam reined asphalt having a normal penetration of 30 to100 mixed with cleaner solvent in the proportion of 40% to 60% cleanersolvent to 60% to 40% asphalt.

The above types of cut back illustrate the range of materials which maybe employed but it will be' understood that in its broad aspect myinvention is not limited to the use of the specic materials mentioned.

In order to satisfy the requirements of various localities and materialsthe types of road oil, asphalt or tar and the percentages of solvent arevaried to produce cut backs having diierent viscosities and diierentcuring properties. The desirability of using cut backs of diilerentviscosities is occasioned principally bythe variation in density ofdiiierent road materials which are to be penetrated (as will behereinafter described) with the cut back.

If the road material is quite dense a cut back having a Sayboltfurolviscosity at '77 Fahrenheit of 30 to 60 may be used. If the roadmaterial is medium in density the viscosity may Inl the manufacture ofmy improved paving according to my improved method the cut back materialis applied to the surface of either loose or compacted road materialwhile the latter is in situ and the material is applied in separateapplications which may approximate 1/8 to 1/4 gallon per square yard andthe material may be applied in any manner which will insure a uniformdistribution. It is not necessary that the material be applied underpressure or be heated. The cut back penetrates or iiows into the roadwaycompletely coating with cut back each particle of aggregate to the fulldepth of penetration.

As soon as one coating is applied evaporation of the solvent starts. Inthis application the material will be deposited through the roadmaterial down to the limit of a first zone which has been indicated at Ain Fig. 3l and which is shown diagrammatically in the particle at I2 inFig. 8. After the solvent has partially passedy from the binder a secondapplication is made. This second application will penetrate to thebottom of zone B in Fig. 3 and will cause a second coating as indicatedat I4 in Fig. 8 to be applied to the upper aggregates and will apply aninitial coating I5 to the aggregate in the second zone.

After a suitable interval the third application is made. In thisapplication the cut back passes down and coats the third zone C applyinga triple coating to the upper aggregates as at I6, double coating I'I tothe aggregates in the second zone and an initial coating I8 to theaggregates in the third zone. A fourth treatment may be then appliedwhich will penetrate to the fourth zone D thus causing a fourth coatingI9 on the upper aggregates, a third coating 20 on the aggregates in thesecond zone, a double coating 2I on the aggregates in the third zone anda single coating 22 on the aggregates in the lower zone.

The number of applications will vary from two to ten or more accordingto the content of the road material and the total amount of out backapplied. In the application of the material as above described the rstcoating is uniformly distributed throughout the aggregates for a smalldistance below the surface in zone A. l The second applicationpenetrates through the aggregates in zone A treated with the firstapplication leaving a second film of cut back on the material treated inzone A with the first application and causing a portion of the secondapplication to penetrate through zone A to zone B which receives itsfirst application.

Each succeeding application results in an additional coating on theupper zones and an initial coating in the lowermost zone. This processof building up layer upon layer has the effect of leaving a heavierdeposit and more binder in the road material nearest the surface and agradually diminishing amount of binder in the zones below the surface.The binder nally deposited in the upper zone is preferably of suchamount as to fill all the voids and to provide a wearingsurface.

In Fig. 2 the roadway IIJ is indicated with a truck wheel 23 shown as inengagement with the roadway as at 24. It is well known that the lines ofpressure of a load which is supported on an appreciable depth of stableroad material will diverge from the point of contact in all directionsat an angle as indicated at 25 in Fig. 2. If the wheel supports a loadof 800 pounds and has a surface of contact longitudinally of one inchand a tire width of four inches, the area of contact 24 is four squareinches and the road material at the surface is subjected to a stress of200 pounds per square inch.

This load before reaching the sub-grade below the paving is distributedover an increased area depending on the depth of the paving. With thefigures just quoted if the depth of material treated is three inches andif the line 25 of divergence of pressure is at 30 to the horizontal, thearea over which the load would be distributed would be approximately33.3 square inches and the road material would be under a stress ofapproximately 24 pounds per square inch.

Thus it will be seen that with my invention the strength of the roaddecreases from the surface downwardly so that where great strength isrequired this is amply provided for While at the same time there is nowaste of material in providing a binder in an area where the loadstresses are light.

From the foregoing it will be apparent that by applying the binder tothe surface as described this binder is disposed in the roadbed invarious amounts and in locations which will produce uniform stability inthe roadbed under stress by diminishing from the surface down. With thearrangement satisfactory treatment of a roadbed for any desired depthwith a less amount of binder is secured or if the same amount of binderis employed the latter is employed to a greater depth so that in eithercase a superior paving results.

Having thus described my invention, I claim:

The method of making a road in situ from granular road forming materialcomprising applying successive applications of approximately 1A to 1A;gallon per square yard of an asphaltic cut back which has a Sayboltfurol viscosity at '77 F. of from 30 to 130 and allowing eachapplication to 'cure partially before making the next applicationwhereby successive applications will penetrate deeper until the upperstratum is completely saturated.

.MILTON H. IRVINE.

